Hydraulic torque amplifier system with variable preamplifier duct orifice cross section



Dec. 10, 1968 SElUEMON lNABA ET AL 3,415,163

HYDRAULIC TORQUR AMPLIFIER SYSTEM WITH VARIABLE PRRAMPLIRIER DUCT ORIFICE CROSS SECTION Filed Feb. 6, 1967 United States Patent O" 3,415,163 HYDRAULIC TORQUE AMPLIFIER SYSTEM WITH VARIABLE PREAMPLIFIER DUCT ORIFICE CROSS SECTION Seiuemon Inaba, Kawasaki-shi, and Ryoko Shirafuji,

Tokyo, Japan, assiguors to Fujitsu Limited, Kawasaki, Japan, a corporation of Japan Filed Feb. 6, 1967, Ser. No. 614,372 IClaims priority, application Japan, Feb. 9, 1966, 41/ 11,003 6 Claims. (Cl. 91-363) ABSTRACT OF THE DISCLOSURE The hydraulic torque amplifier system has an hydraulic preamplifier component for imparting a given pressure to a ow of hydraulic fluid therethrough in response to a given torque applied thereto, an hydrualic fluid servomotor component responsive to the pressure of the hydraulic fluid flow for producing a mechanical movement at a speed substantially proportional to the pressure, and a feedback component for detecting the speed of the mechanical movement and reducing the pressure of the hydraulic fiuid flow in proportion to the speed of the mechanical movement. The preamplifier component includes an hydraulic fiuid duct system provided with orifices having fixed cross sections and having variable cross sections. The servomotor component includes a four-directional pilot valve and an hydraulic motor. The feedback component includes a tachometer generator which produces an output signal proportional to the detected speed of the mechanical movement, the output signal actuating a torque motor to control a pressure control valve for varying the pressure of the hydraulic fluid flow in proportion to the output signal.

Our invention relates to mechanism for amplifying the output torque of a control motor having a small output, such as an electric pulse or step motor for example, by means of an hydraulic servomechanism or torque amplifier system employing oil or hydraulic fluid pressure.

In an hydraulic torque amplifier system of this general type, there occurs a lag (so-called transfer lag) between the output signal and the input signal. It is most desirable that this lag be kept as small as possible. The hydraulic torque amplifier system or servomechanism is made up of several component devices that are connected to one another, and the simplest method of reducing the lag between output and input signals is to increase the sensitivity or gain of each of the component devices. However, if the sensitivity or gain of each component device is merely increased, the servornechanism reaches an unstable state. A result thereof is that when the input signals are applied in steps, the output, for example a rotation, tends to overshoot rather greatly and consequently a relatively long stabilization period is required.

It is accordingly an object of our invention to provide hydraulic torque amplifier system which avoids the aforementioned disadvantage of the heretofore know amplifier systems of this type and, more particularly, which provides torque amplifier system operating by oil pressure that is stable and that has a very rapid response.

In furtherance of these objects, it is consequently our objective to provide each component of the torque amplifier system with proper sensitivity, giving due consideration to the fact that it is inherently impossible to shorten the transmission delay between input and output below a certain finite value.

With the foregoing and other objects in View, we provide in accordance with our invention, hydraulic torque amplifier system comprising hydraulic preamplifier means 3,415,163 Patented Dec. 10, 1968 ICC for imparting a given pressure to a fiow of hydraulic fluid therethrough in response to a given torque applied thereto, hydraulic fluid servomotor means responsive to the pressure of the hydraulic fluid flow for producing a mechanical movement at a speed substantially proportional to the pressure, and feedback means for detecting the speed of the mechanical movement and reducing the pressure of the hydraulic fiuid flow in proportion to the speed.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in hydraulic torque amplifier system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirt of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of a specific embodiment when read in connection with the accompanying drawing in which:

FIG. 1 is a partly diagrammatic and partly sectional view of an hydraulic or oil pressure torque amplifier system constructed in accordance with the present invention.

FIG. 2 is a view taken along the lines II-II of FIG. l;

FIG. 3 is a view taken along the lines III- III of FIG. l;

FIG. 4 is a block diagram of the torque amplifier system of FIG. l; and

FIG. 5 is a diagrammatic view of a torque motor constituting one of the components of the torque amplifier system of FIG. 1.

Referring now to the drawings and first particularly to FIG. l thereof, there is shown a control motor 1 of relatively small output such as, for example, an electric pulse or step motor, which produces an output torque that is transmitted by intermeshing spur gears 2 and 3 to an input shaft 4. The shaft 4 has a disc 7 attached to an end thereof which, as shown in FIG. 2, has a pair of bores or windows 6 and 7 formed therein and located in the disc in spaced diametrically opposing positions. The disc is maintained in close engagement with the end surface 5 of a shaft 9 located coaxial to the disc 5 and mounted for smooth rotation within a bore 44 in a housing 8. The engaging surface of the disc 5 and the surface 5 of the shaft 9 have a relatively smooth finish so that they can rotate and slide smoothly on one another Within the bore 44 in the housing 8. The shaft 9 is mechanically connected with the output shaft 11 of an hydraulic motor 10 and is rotatable together therewith so that it is possible to consider both the shafts 9 and 11 to act in fact as one rotatable body.

As shown in FIG. 3, a pair of substantially semilunar slots 12 and 13 are formed in the end surface 5 of the shaft 9. The slots 12 and 13 are spaced symmetrically from a diameter of the shaft 9, i.e. the horizontal diameter .,seen in FIG 3. Referring again to FIG 1, the slots 12 and 13 respectively communicate with circumferential grooves 16 and 17, formed around the bore 44, through oil ducts 14 and 15 respectively provided in the shaft 9.

As shown in FIG. 3, the slots 12 and 13 have a gradually varying width from one end thereof to the other. In the assembled view of FIG. l, the semilunar slots 12 and 13 form conjointly with the respective windows 6 and 7 a pair of orifices having variable cross section for the fiow yof oil therethrough. The housing 8 is also provided with a number of oil ducts. A pair of branching ducts 20 and 21 communicate respectively with the circumferential grooves 16 and 17 and are respectively provided with xed orifice plates or the like for reducing the flow cross section therewithin. On the other side of the orifice plates 18 and 19 from the junction of the ducts 20 and 21 with the circumferential grooves 16 and 17 respectively, the ducts and 21 are connected conjointly with a duct 22 communicating with a circumferential groove 23 formed in a cylindrical chamber 80 also provided within the housing 8.

A cylindrical piston member having three axially spaced piston portions 24, 24' and 24" connected to one another by a shaft 81 of reduced diameter is slidably disposed in the cylindrical chamber 80. Besides the circumferential groove 23, additional circumferential grooves 25 and 26 are provided in the cylindrical chamber 80 axially spaced respectively from the circumferential groove 23. The piston member 24, 24', 24" is axially displaceable within the cylindrical chamber 80 and, together with the chamber 80 and the circumferential grooves 23, 25 and 26, functions as a four-directional pilot valve. Hydraulic fluid or oil under pressure suitably supplied by the action of the four-directional pilot valve effects rotation of the shaft 9 and the shaft 11 of the hydraulic motor 10. Coaxially disposed 4helical springs 27 and 28 located between both extremities of the piston member 24, 24', 24" and the end walls of the chamber 80 are provided for restoring the piston member to the neutral position thereof shown in FIG. l when not subjected to Iunbalanced force.

An hydraulic fluid or oil inlet communicates with the circumferential groove 23 through a duct 29. As represented by the arrow pointing into the inlet 30, the oil or hydraulic uid is supplied under suitable pressure from a source thereof not shown in the figures. An hydraulic fluid or oil outlet 33 discharges the oil or hydraulic fluid from the circumferential grooves 26 and 25 respectively through a duct 32 and a duct 31 connected therewith. The outlet 33 can be suitably connected to the return inlet of the source of hydraulic uid or oil which, as aforementioned, is not shown in the drawing.

As seen in FIG. 1, the cylindrical chamber 80 with the piston member disposed therein is subdivided into four oil-receiving chambers, two of which are end chambers 40 and 41 in which the springs 27 and 28 respectively are located and two of which are intermediate chambers 34 and 35 in which portions of the shaft 81 are located. The oil chambers 34 and 35 respectively communicate through ducts 36 and 37 with openings 38 and 39 in the hydraulic motor 10 which alternately serve as oil outlets or inlets in accordance with the operation of the motor 10. The end chambers 40 and 41 of the four-directional pilot valve are respectively connected to the oil ducts 20 and 21 through respective connecting ducts 42 and 43. The disc 5 is located within a chamber formed at an end of the bore 44 in the housing 8 which is in communication with the circumferential groove 24 through oil duct 45.

The end chambers 40 and 41 are also connected, by means of the oil ducts 46 and 47 respectively, with respective circumferential grooves 48 and 49 formed in a chamber 82 of a needle-type valve also provided in the casing 8. The circumferential grooves 48 and 29 and a needle member 50 slidable axially in the chamber 82 together form a pressure control valve for controlling the pressure in the end chambers 40 and 41 of the four-directional pilot valve. Thus, the oil pressure acting on the piston 24, 24', 24" varies in accordance with the displacement of the needle member 50 from its illustrated position in FIG. 1.

A torque motor 52 is connected by a pus-h rod 51 with the needle member 50, the push rod 51 and needle member 50 being displaceable together a distance proportional to an input voltage supplied to the torque motor 52. End chambers 53 and 54 located on both sides of the needle member 50 are connected by converging ducts 55 and 56 with the oil duct 32.

In accordance with the invention, a tachometer -or r.p.m. generator 57 is rotatable in accordance With the output shaft 11 of the hydraulic motor 10 and produces an output voltage that is proportional to the speed of rotation of the output shaft 11. In FIG. 1 there is shown by Way of example a tachometer generator 57 which is connected with a feed screw 59 of a diagrammatically illustrated machine 58 that is driven by the output shaft 11. The output voltage signal of the tachometer generator 57 is conducted by the lead 60 to an amplifier 61 and from there with increased amplitude is delivered as input voltage by the lead 62 to the torque motor 52. In accordance with the strength of the input voltage thus applied to the torque motor 52, the needle member 50 is displaced proporlionately to the speed of rotation of the output shaft 11 of the hydraulic motor 10.

FIG. l illustrates the neutral condition of the hydraulic torque amplifier of the present invention. In the neutral condition, the control motor 1 is stationary and the crosssectional areas of the openings provided by the registry of the slots 12 and 13 respectively and the windows 6 and 7 provided in the disc 5 are equal. The output shaft 11 of the lhydraulic motor 10 is thus also stationary.

When the torque amplifier is in its neutral condition, the pressure oil which had entered from the oil inlet 30 passes through the sections of reduced cross-sectional area 18 and 19 and is accordingly reduced in pressure. The oil also flows through the slots 12 and 13 and is thereby even further reduced in pressure, the cross-sectional areas of the openings provided by the slots 12 and 13, aligned respectively with the windows 6 and 7, being equal to one another. After flowing through the slots 12 and 13 and windows 6 and 7 respectively, the oil is then discharged into the end space of the bore 44 which is subjected to atmospheric pressure. Starting from the neutral position thereof, when the control motor 1 is rotated through a predetermined angle, for example in the direction of the arrow shown in FIG. 1 on the shaft of the motor 1, the shaft 4 and the disc 5 attached thereto are rotated through that angle in the opposite rotary direction and the cross-sectional area of the opening provided by the aligned slot 12 and the window 6 decreases whereas the area of the opening provided by the aligned slot 13 and window 7 increases. Thus, the hydraulic uid or oil pressure in the duct 20 between the reduced section 18 and the circumferential groove 16 communicating with the slot 12 is increased, while the oil pressure in the duct 21 located between the reduced section 19 and the circumferential groove 17 communicating with the slot 13 is reduced. The principle of pressure variation is in essence equivalent to the principle of back-pressure variation in a conventional nozzle and flapper mechanism.

Due to the oil pressure increase in the duct 20 and the oil pressure decrease in the duct 21, the pressure of the oil in the end space 40 of the four-directional pilot valve increases and the pressure of the oil in the end space 41 of that valve decreases. The piston member 24, 24', 24" is then subjected to a focre in the direction of the arrow superimposed thereon in FIG. 1 and is accordingly displaced in the direction of that arrow to a position in which the force applied to the piston member is counterbalanced by the restoring force of the springs 27 and 28. This action is in principle equivalent to the conventional method of operating a four-direction pilot valve utilizing the backpressure of a nozzle and flapper mechanism.

When the piston member 24, 24', 24" is displaced in the direction indicated in FIG. 1, the pressure fluid or oil supplied through oil inlet 30 flows to the oil inlet 38 of the hydraulic motor 10 through intermediate chamber 34 and the duct 36 and causes the output shaft 11 of the hydraulic motor and the shaft 9 joined theerto to rotate. The returning fluid or oil discharged from the hydraulic motor 10 flows from the outlet opening 30 provided therein through duct 37 and the intenmediate chamber 35 to the oil outlet 33 and is yaccordingly returned to its nonillustrated source. This principle of operation is the conventional principle of driving a hydraulic motor by means of a four-directional pilot valve.

If the hydraulic motor is so constructed `that it provides rotation of the rotary shaft 11 and the shaft 9 connected thereto in the direction of the arrow superimposed thereon in FIG. l, the difference between the area of the opening formed by the slot 12 and the window 6, on the one hand, and the larea of the opening formed by the slot 13 and the window 7, on the other hand, which is produced by rotation of the disc 5, is thus eliminated. When the areas of both these openings thus become equal to one another, the torque amplifier of this invention is restored to its neutral condition of FIG. 1 and the output shafts 9 and 11 become stationary.

As the output shaft 11 rotates in the aforedescribed manner, an output voltage proportional to the speed of rotation thereof is generated by the tachometer generator 57, which may be of conventional construction, and this output voltage, when suitably amplified and fed to the torque motor 52, causes the latter to displace the needle member 50 a distance proportional to the speed of rotati-on of the output shaft 11.

If the arrangement is such that the needle member 50 is being displaced in the direction of the arrow superimposed thereon in FIG. 1 at the particular moment, the pressure in the end chamber 40 is accordingly reduced as the output shaft 11 is rotating.

The aforedescrilbed operating principles can perhaps best be summarized by the block diagram of FIG. 4 in which an oil pressure preamplifier unit or device 63 is shown receiving an input 64 which is the relative angular displacement between the disc 5 and the shaft 9 or the output shaft 11 connected thereto, the output 65 from the pressure preamplifier element 63 is the oil pressure acting on the piston member 24, 24', 24" when the needle member 50 is stationary. An hydraulic fluid or oil pressure servomotor unit or device 66 represents the four-directional pilot valve and the hydraulic motor 10, the input 67 thereto being the oil pressure acting on the piston member 24, 24', 24, and the output 68 thereof being the angle of rotation of the output shaft 11 or the shaft 9 affixed thereto. A tachometer generator feedback unit or device 69 and the output 70 thereof represent the volt- -age generated in proportion to the speed of rotation of the output shaft 11 for the purpose of reducing the pressure acting on the piston member 24, 24', 24". The input 71 to the system shown in FIG. 4 represents the angle of rotation of the disc 5. When the hydraulic fluid of oil pressure torque amplifier system of this invention is considered as being made up of the oil pressure preamplifier unit 63, the oil pressure servomotor unit 66 and the tachometer generator feedback unit 69 described hereinbefore with regard to FIG, 4, and the transfer characteristic between the input `and output of each of these elements is taken into consideration, it is noted that the oil pressure preamplifier unit 63 is a proportionating device virtually without any time lag between input and output signals. the oil pressure servometer unit 66 is an integrating device having a time lag greater than the first degree, i.e. exponential, and the tachometer generator feedback unit 69 is virtually a differentiating device. It will therefore be assumed herein that the lag in transmission between input and output of the torque lmotor 52 forming part of the feedback unit 69 can be ignored when compared with the lag in transmission of the oil pressure servomotor unit 66.

The response characteristic of the angle of rotation 68 of the output shaft 11 as compared to the angle of rotation 71 of the disc 5 will now be considered. Assuming that the tachometer generator feedback unit 69 were not included in the amplifier system of this invention, when the sensitivity or gain of the oil pressure preamplifier unit 63 or the oil pressure servomotor unit 66 is increased in order to reduce the. lag between the output 68 and the input 71, the system, without the feedback, tends to oscillate and consequently cannot be put to practical use. The cause of the oscillation is basically the transmission lag occurring within the oil pressure servomotor unit 66.

When, however, the tachometer generator feedback element 69 is employed in the system as in accordance with the invention herein, it can readily be seen from consideration of tachometer feedback theory that the transmission lag within the oil pressure servomotor unit 66 is clearly reduced. Consequently, even when the sensitivity or gain of the oil pressure preamplifier funit 63 is greatly increased, the resulting system provided by the invention herein does not oscillate, and it consequently becomes possible to provide a hydraulic fluid or oil pressure torque amplifier system that is stable on the whole and has little lag between the initial input and the eventual output thereof.

It :should of course be apparent that instead of the method of controlling the pressure of the end chamber 40 or 41 by detecting the speed 0f rotation of the output shaft 11 with a tachometer generator 57 and accordingly displacing the needle member 50 by means of a torque motor 52 connected between the tachometer generator 57 and the needle member 50 as described hereinabove, the pressure of the end chamber 40 or 41 can als-o be controlled by varying the -degree of reduction of the area of the fixed orifice plate 18 or 19. Moreover, the rotary speed of the output shaft 11 need not be detected only by a tachometer generator 57 but can also be detected by suitable mechanical means. A preferred embodiment as shown in FIG. 1 of the drawings, in any event, is stable and exhibits relatively little transfer lag between input thereto and output thereof.

By way of example, FIG. 5 shows diagrammatically a torque -motor 52 which effects linear displacement of the push rod 51 and the needle member 50, accordingly, of the pressure control valve of the invention. As shown in FIG. 5, a signal is applied from the amplifier 61 to a center-tapped coil H which is wound on one half of a yoke Y2 which is connected by permanent magnets PM1 and PM2 with the second half of a yoke Y1. Depending upon the direction of rotation of the shaft 11, the signal from the tachometer generator 57 will be negative or positive and the armature AR of the torque motor 52 will accordingly rotate in one or the other rotary direction due to the ux created in the magnets PM, and PM2 and across `the respective gaps of the yoke halves Y1 and Y2 as shown in FIG. 5. The armature AR carries a lever L rigidly secured thereto and pivotable in accordance with the direction of turning of the armature AR. The lever arm L is in Iturn pivotally connected with the needle valve push rod 51. As can be readily seen, a signal from the tachometer generator 57 isamplified by the amplifier 61 and energizes the coil H causing the armature AR to pivot and to linearly displace thepush rod 51 and needle member 50 in accordance with the direction of turning of the armature. Then notch N is provided in the yoke half Y1 to afford clearance for the travel of the lever L.

We claim:

1. Hydraulic torque amplifier system comprising hydraulic preamplifier means for imparting variable pressure to a fiow of 'hydraulic fluid therethrough in response to a given torque applied thereto, hydraulic fluid servomotor means responsive to said pressure of said hydraulic fluid flow for producing a mechanical movement at a speed substantially proportional to said pressure, and feedback means for detecting the speed of said mechanical movement and reducing the pressure of said hydraulic fluid flow in proportion to said speed, said preamplifier means comprising duct means for circulating a supply of hydraulic fiuid, said duct means having orifice means of fixed cross section for reducing the pressure of the hydraulic fluid in part of saidduct means downstream from said orifice means a fixed cross section, orifice means of variable cross section located at the upstream end of said part of said duct means, input means for providing an input torque, means for varying the cross section of said orifice means of variable cross section in response to said input torque whereby the pressure of the hydraulic uid in said part of said duct means is varied, said means for varying the cross section of said orifice means comprising a disc mounted for rotation about its axis, coupling means for coupling said input means to said disc and a shaft coaxially mounted with said disc for rotation about its axis, said shaft having an end surface in close proximity with said disc, said orifice means being a pair of windows formed in said disc and a pair of slots formed in the end surface of said shaft in spaced relation to each other and having respectively a substantially crescent configuration with varying radial width, said windows and said slots being respectively in registry and cooperative to provide openings of variable cross section in response to relative angular displacement of said disc and said shaft.

2. Hydraulic torque amplifier system according to claim 1, wherein said duct means comprises a first d'uct portion connected through said shaft with one of said slots, and a second duct portion connected through said shaft with the other of said slots.

3. Hydraulic torque amplifier system according to claim 2, wherein said hydraulic iiuid servomotor means comprises a pilot valve and a hydraulic motor, said pilot valve comprising a valve chamber having a pair of opposite end spaces and a pair of intermediate spaces and a piston member mounted in said valve chamber for axial displacement therein, inlet duct means for supplying iiuid under pressure to said valve chamber, and outlet duct means for discharging fluid from said valve chamber, duct means communicating respectively between said first duct portion and one of said pilot valve end spaces on the one `hand and between said second duct portion and the other of said pilot valve end spaces on the other hand, and duct means respectively communicating between said pilot valve intermediate spaces and said Ihydraulic motor for rotating the shaft of said motor in accordance with the pressure of hydraulic fluid therein.

4. Hydraulic torque amplifier system according to claim 3, wherein said feedback means comprises a tachometer generator operatively connected with the shaft of said hydraulic motor for producing a signal varying in value with the speed of rotation of said hydraulic motor shaft, a torque motor operatively connected with said tachometer generator and actuable in response to said signal therefrom, and a pressure control valve comprising a chamber having a pair of end spaces, and a valve member disposed in said chamber and operatively connected to said torque motor for axial displacement in said chamber, said end spaces in said pressure control communicating respectively with the end spaces of said pilot valve chamber on the one hand and with said outlet duct means on the other hand.

5. Hydraulic torque amplifier system according to claim 4, wherein an amplifier is connected between said tachometer generator and said torque motor for amplifying the signal produced by said generator and passing the amplified signal to said motor.

6. Hydraulic torque amplifier system according to claim 4, including a unitary housing, said hydraulic preamplifier means, substantially all of said duct means, said pilot valve, part of the shaft of said hydraulic motor, and said pressure control valve are housed in said housing.

References Cited UNITED STATES PATENTS 2,939,430 6/1960 Westbury 91-364 2,977,765 4/1961 Fillmore 91363 3,016,883 1/1962 Faisander 91--364 3,182,561 5/1965 Arnett 91-364 FOREIGN PATENTS 358,334 12/1961 Switzerland. 1,283,750 12/1961 France.

PAUL E. MASLOUSKY, Primary Examiner.

U.S. Cl, X.R. 

